1. Field of the Invention
The present invention relates to a driving circuit and a driving method of a color liquid crystal display, and a color liquid crystal display device; and more particularly to the driving circuit of the color liquid crystal display adapted to drive the color liquid crystal display based on digital video data to which a gamma correction has been made, the display device having such the driving circuit of the color liquid crystal display, and the method for driving the color liquid crystal display.
The present application claims priority of Japanese Patent Application No.2000-353427 filed on Nov. 20, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 17 is a schematic block diagram showing an example of configurations of a conventional driving circuit of a color liquid crystal display 1 disclosed in Japanese Laid-open Patent Application No. 2001-134242 published on May 18, 2001 later than the filing date of Japanese Patent Application No. 2000-353427 corresponding to the present application (Therefore, Japanese Laid-open Patent Application No. 2001-134242 has not a qualification as a prior art reference.)
The disclosed color liquid crystal display 1 is of a type of color liquid crystal display that is driven by an active-matrix driving method and that uses, for example, a TFT (Thin Film Transistor) as a switching element. Pixels are disposed in a region surrounded by a plurality of scanning electrodes (gate lines) mounted at predetermined intervals in a row direction and by a plurality of data electrodes (source lines) mounted at predetermined intervals in a column direction. Each of the pixels has a liquid crystal cell being equivalently a capacitive load, the TFT used to drive a corresponding liquid crystal cell and a capacitor used to accumulate a data charge during one vertical sync period. By applying a data red signal, data green signal, and data blue signal to be produced, based on red data DR, green data DG, and blue data DB being digital video data, to the data electrode and, at the same time, by applying scanning signals to be produced based on a horizontal sync signal and a vertical sync signal to the scanning electrode, a color character, color image or a like is displayed (though not shown in FIG. 17). Moreover, the disclosed color liquid crystal display 1 operates in a so-called xe2x80x9cnormally black modexe2x80x9d in which transmittance or luminance of light obtained when an off-driving voltage is applied is lower than those obtained when the on-driving voltage is applied.
As shown in FIG. 17, the disclosed driving circuit of the color liquid crystal display 1 chiefly includes a control circuit 2, a gray scale power circuit 3, a data electrode driving circuit 4, and a scanning electrode driving circuit 5.
The control circuit 2 is made up of, for example, ASICs (Application Specific Integrated Circuits) and is adapted to feed 8 bits of red data DR, 8 bits of green data DG, and 8 bits of blue data DB supplied from an outside to the data electrode driving circuit 4 and, at the same time, to produce a horizontal scanning pulse PH, a vertical scanning pulse PV, and a polarity reversed pulse POL used to drive the color liquid crystal display 1 with alternating current, based on the horizontal sync signal and vertical sync signal, and to feed these pulses to the data electrode driving circuit 4 and the scanning electrode driving circuit 5. Moreover, the control circuit 2 feeds a red gray scale voltage data DGR, a green gray scale voltage data DGG, and a blue gray scale voltage data DGB obtained by making an individual and separate gamma correction to each of the red data DR, green data DG, and blue data DB to provide gray scales, to the gray scale power circuit 3. Moreover, the gamma correction employed in the embodiment includes one gamma correction (hereinafter referred to as a first gamma correction) in which the correction is made to arbitrarily provide a characteristic of luminance required in reproduced images to luminance of input images and another gamma correction (hereinafter referred to as a second gamma correction) that is made to match an xe2x80x9capplied voltagexe2x88x92transmittancexe2x80x9d characteristic (hereinafter as a Vxe2x88x92T characteristic) for each of the red, green, and blue colors used in the color liquid crystal display 1.
The gray scale power circuit 3, as shown in FIG. 18, includes digital/analog converters (DACs) 111 to 113 and voltage followers 121 to 1254. The DAC 111 converts the red gray scale data DGR fed from the control circuit 2 into analog red gray scale voltages VR0 to VR17 and feeds them to the voltage followers 121 to 1218, respectively. Similarly, the DAC 112 converts the green gray scale data DGG fed from the control circuit 2 into analog green gray scale voltages VG0 to VG17 and feeds them to the voltage followers 1219 to 1236, respectively. The DAC 113 converts the blue gray scale data DGB fed from the control circuit 2 into analog green gray scale voltages VB0 to VB17 and feeds them to the voltage followers 1237 to 1254, respectively. The voltage followers 121 to 1254 feed the red gray scale voltages VR0 to VR17, the corresponding green gray scale voltages VG0 to VG17, and the blue gray scale voltages VB0 to VB17, which are all used for making the gamma correction, as they are, to the data electrode driving circuit 4.
The data electrode driving circuit 4 is made up of k pieces (xe2x80x9ckxe2x80x9d being a natural number) of data electrode driving sections 41 to 4k. Each of the data electrode driving sections 41 to 4k makes the gamma correction, based on red gray scale voltages VR0 to VR17, green gray scale voltages VG0 to VG17, and blue gray scale voltages VB0 to VB17 fed from the gray scale power circuit 3, to the red data DR, green data DG, and blue data DB each corresponding to each of data electrodes mounted in the color liquid crystal display 1, out of the red data DR, the green data DG, and the blue data DB fed from the control circuit 2, in order to provide gray scales, and converts the gamma-corrected data into 384 pieces of analog data signals and then outputs them. For example, when the color liquid crystal display 1 is of a type of SXGA (Super Extended Graphics Array) which provides 1280xc3x971024 pixel resolution, since one pixel is made up of three dot pixels including a red (R) dot pixel, a green (G) dot pixel, and a blue (B) dot pixel, the number of dot pixels becomes 3840xc3x971024. Therefore, in the example, the data electrode driving circuit 4 is made up of ten pieces of data electrode driving sections 41 to 410 (3840 pieces of pixels÷384 pieces of data signals). Since all of the data electrode driving sections 41 to 410 have the same configurations except that each of their components and each of input and output signals have a different subscript, a description of only the data electrode driving section 41 will be provided below.
FIG. 19 is a schematic block diagram showing an example of configurations of the data electrode driving section 41. As shown in FIG. 19, the data electrode driving section 41 chiefly includes multiplexers (MPXs) 131 to 133, DACs 141 to 143 (of an 8 bit-data conversion type), and voltage followers 151 to 15384. The MPX 131 switches a set of red gray scale voltages VR0 to VR8 or a set of red gray scale voltages VR9 to VR17, out of red gray scale voltages VR0 to VR17 fed from the gray scale power circuit 3, based on a polarity reversed pulse POL fed from the control circuit 2 and feeds the switched voltages to the DAC 141. Similarly, the MPX 132 switches a set of red gray scale voltages VG0 to VG8 or a set of green gray scale voltages VG9 to VG17, out of green gray scale voltages VG0 to VG17 fed from the gray scale power circuit 3, based on the polarity reversed pulse POL fed from the control circuit 2 and feeds the switched voltages to the DAC 142. The MPX 132 switches a set of red gray scale voltages VB0 to VB8 or a set of green gray scale voltages VB9 to VB17, out of green gray scales VB0 to VB17 fed from the gray scale power circuit 3, based on the polarity reversed pulse POL fed from the control circuit 2 and feeds the switched voltages to the DAC 143.
The DAC 141 makes the gamma correction, based on the set of red gray scale voltages VR0 to VR8 or the set of the red gray scale voltages VR9 to VR17 fed from the MPX 131, to 8 bits of the red data DR fed from the control circuit 2 in order to provide gray scales and, after having converted the gamma-corrected data to analog data red signals, feeds them to the corresponding voltage followers 151, 154, 157, . . . , 15382. Similarly, the DAC 142 makes the gamma correction, based on the set of green gray scale voltages VG0 to VG8 or the set of the green gray scale voltages VG9 to VG17 fed from the MPX 132, to 8 bits of the green data DG fed from the control circuit 2 in order to provide gray scales and, after having converted the gamma-corrected data to analog data red signals, feeds them to the corresponding voltage followers 152, 155, 158, . . . , 15383. The DAC 143 makes the gamma correction, based on the set of blue gray scale voltages VB0 to VB8 or the set of the blue gray scale voltages VB9 to VB17 fed from the MPX 133, to 8 bits of the blue data DB fed from the control circuit 2 in order to provide gray scales and, after having converted the gamma-corrected data to analog data red signals, feeds them to the corresponding voltage followers 153, 156, 159, . . . , 15384. The voltage followers 151 to 15384 apply the corresponding data red signal, data green signal, and data blue signal fed from the DAC 141 to 143 to the corresponding data electrode in the color liquid crystal display 1.
The scanning electrode driving circuit 5 shown in FIG. 17 produces scanning signals with the timing when the vertical scanning pulse PV is fed from the control circuit 2 and sequentially feeds the produced signals to corresponding scanning electrodes in the color liquid crystal display 1.
In the display device of the color liquid crystal display 1 provided with the driving circuit of the color liquid crystal display 1 having configurations described above, as shown in FIG. 20, the control circuit 2 and the gray scale power circuit 3 are mounted on a printed circuit board 16 while the data electrode driving sections 41 to 410 are mounted on ten pieces of film carrier tapes electrically connecting the printed circuit board 16 to the color liquid crystal display 1, that is, they are packaged in a form of TCPs (Tape Carrier Packages) 171 to 1710. As shown in FIG. 21, the printed circuit board 16 is attached to an upper portion of a rear of a backlight 18 being approximately wedge-shaped in cross section which is attached to a rear of the color liquid crystal display 1. The backlight 18 has a point light source such as a white bulb or a like or a line light source such as a fluorescent lamp or a like, and a light diffusing member used to diffuse light emitted from these light sources to produce flat light and is adapted to uniformly illuminate the rear of the color liquid crystal display 1 from a rear side of the color liquid crystal display 1 being a non-light emitting display device.
The conventional color liquid crystal display 1 has a problem. That is, as described above, in the driving circuit of the conventional color liquid crystal display 1, since the gray scale power circuit 3 and the data electrode driving sections 41 to 410 are mounted individually and separately from each other, it is necessary to feed 54 pieces of gray scale voltages including the red gray scale voltages VR0 to VR17, green gray scale voltages VG0 to VG17, and blue gray scale voltages VB0 to VB17 to each of ten pieces of the data electrode driving sections 41 to 410. Two methods for feeding such gray scale voltages are available, however, each of them has a shortcoming as described below.
A first method is to form 54 pieces of wirings on a surface layer of the printed circuit board 16 and to connect each of the wirings to each of the TCPs 171 to 1710. A pitch between the wirings being employed generally and presently is 1.27 mm. If, therefore, 54 pieces of wirings are to be formed, using the above pitch, on the surface layer of the printed circuit board 16, a depth of the printed circuit board 16 becomes longer by 2 cm or more, compared with a case where 54 pieces of gray scale voltages including the red gray scale voltages VR0 to VR17, green gray scale voltages VG0 to VG17, and blue gray scale voltages VB0 to VB17 are transferred serially using one wiring (refer to FIG. 20). This causes, as shown in FIG. 21, an area in which the printed circuit board 16 is mounted on the upper portion of the rear of the backlight 18 to become wider. Generally, the backlight 18 plays not only a part in illuminating uniformly the rear of the color liquid crystal display 1 but also a part in keeping a rear portion of the display device plane and can be used commonly for any color liquid crystal display 1 so long as it has the same screen in size. However, if the depth of the printed circuit board 16 is different in every type of the color liquid crystal display 1, that is, in every resolution that the color liquid crystal display 1 can provide, it is necessary to change a shape of the backlight 18 for every type of the color liquid crystal display 1, that is, every resolution to be provided by the color liquid crystal display 1, which causes an increase in costs of the display device.
The limit pitch between terminals of the typical TCP being presently employed is 300 xcexcm when considerations are given to a level of pressure-based contact technology by which each of terminals of the TCP is put in contact with each of terminals of the printed circuit board 16 by using external pressure in order to obtain electrical conductivity. Therefore, if each of terminals being connected to 54 pieces of wirings formed on the surface layer of the printed circuit board 16 is connected to each of terminals formed on upper portions of the TCP 171 to 1710 by using the pressure-based contact technology, each of widths WT of the TCP 171 to 1710 becomes larger by 1.6 cm or more (refer to FIG. 20). As a result, in the case of the 18-inch type color liquid crystal display of the SXGA type in which ten pieces of the data electrode driving sections 41 to 410 have to be placed, since the fitting width for the TCP 171 to 1710 becomes larger by 16 cm or more, there is a danger that it becomes physically impossible to mount ten pieces of the TCP 171 to 1710 in alignment in a direction of the width WP of the printed circuit board 16 (see FIG. 20).
A second method is to form 54 pieces of wirings in an inner layer of the printed circuit board 16 and to connect each of them to each of the TCP 171 to 1710. In this case, in order to connect the 54 pieces of wirings formed in the inner layer of the printed circuit board 16 to each of terminals formed on the upper portions of the TCP 171 to 1710, the 54 pieces of wirings formed in the inner layer of the printed circuit board 16 have to be connected to 54 pieces of terminals formed via through holes on the surface layer of the printed circuit board 16 and being corresponded to the 54 pieces of wirings. Since a diameter of a typical through hole being presently employed is 0.8 mm, if the 54 pieces of such the through holes having the diameter of 0.8 mm are to be formed on the printed circuit board 16 in alignment, an area required for forming all the through holes has to become wider accordingly.
In both the first and second methods described above, if the number of gray scale voltages including the red gray scale voltages VR0 to VR17, green gray scale voltages VG0 to VG17, and blue gray scale voltages VB0 to VB17 is different, the pitch between wirings, depth DP of the printed circuit board 16, width WT of each of the TCP 171 to 1710 are different and, therefore, the printed circuit board 16 and the TCP 171 to 1710 have to be fabricated in a manner so as to meet the requirement in dimensions, which causes a big increase in costs of the display device.
In view of the above, it is an object of the present invention to provide a driving circuit of a color liquid crystal display which is capable of reducing a substrate packaging area, using a common substrate or TCP even when a resolution and/or the number of gray scale voltages that the color liquid crystal display provides are different, which enables the substrate, TCP, and a display device to be fabricated at low costs. It is also another object of the present invention to provide a color liquid crystal display device using the driving circuit described above and a method for driving the color liquid crystal display.
According to a first aspect of the present invention, there is provided a driving circuit of a color liquid crystal display including:
a data electrode driving circuit to drive the color liquid crystal display by using a gray scale voltage selected based on a video signal out of a plurality of gray scale voltages; and
wherein the data electrode driving circuit produces a plurality of the gray scale voltages corresponding to a gray scale voltage characteristic based on digital gray scale voltage setting data to be supplied.
According to a second aspect of the present invention, there is provided a driving circuit of a color liquid crystal display for driving the color liquid crystal display by using a data red signal, a data green signal, and a data blue signal obtained by making an individual gamma correction to red data, green data, and blue data being digital video data in order to make corrections so that each of the red data, the green data, and the blue data matches a transmittance characteristic of each of a red color, a green color, and a blue color for a voltage applied in the color liquid crystal display, the driving circuit including:
a control circuit mounted separately from the color liquid crystal display and to output, during an invalid period having no bearing on a displaying period for the digital video data, information about the gamma correction to be made to the red data, the green data, and the blue data; and
a data electrode driving circuit mounted in a vicinity of the color liquid crystal display and to drive the color liquid crystal display by using the data red signal, the data green signal, and the data blue signal obtained by making the gamma correction to the red data, the green data, and the blue data, based on information about the gamma correction to be made to the red data, the green data, and the blue data.
In the foregoing, a preferable mode is one wherein the control circuit is mounted on a printed circuit board attached to an upper portion of a rear of a backlight placed on a rear of the color liquid crystal display and wherein the data electrode driving circuit includes a plurality of data electrode driving sections to provide gray scales by making the gamma correction to the red data, the green data, and the blue data each corresponding to each of data electrodes of the color liquid crystal display, out of the red data, the green data, and the blue data and converts the gamma-corrected red data, the gamma-corrected green data, and the gamma-corrected blue data into an analog data red signal, an analog data green signal, and an analog data blue signal, such that the analog data red signal, the analog data green signal, and the analog data blue signal are output, and wherein each of the plurality of the data electrode driving sections is mounted on a corresponding film carrier tape connecting the printed circuit board to the color liquid crystal display.
Also, a preferable mode is one wherein the information about the gamma correction to be made to the red data, the green data, and the blue data, is made up of gray scale information to provide an instruction as to which gray scale voltage should be selected out of the gray scale voltages for the red data, the green data, and the blue data, and of gray scale voltage information to provide an instruction as to which gray scale voltage should be selected out of the plurality of the gray scale voltages.
Also, a preferable mode is one wherein the control circuit feeds the gray scale information and the gray scale voltage information to the data electrode driving circuit as serial data.
Also, a preferable mode is one wherein each of the data electrode driving sections includes:
a shift register to convert the serial data into parallel gray scale information and parallel gray scale voltage information, such that the parallel gray scale information and the parallel gray scale voltage information;
a storing section to store, in advance, a selection signal to provide an instruction as to which gray scale voltage should be selected as a plurality of gray scale voltages for the red data, the green data, and the blue data;
a decoder to decode the gray scale information and to output selection information to provide an instruction as to which gray scale voltage should be selected out of the plurality of the gray scale voltages for the red data, the green data, the and blue data;
a multiplexer to select any one of the gray scale voltgage based on the selection signal read from the storing section according to the selection information and to output the selected gray scale voltage as a plurality of red gray scale voltages, green gray scale voltages, and blue gray scale voltages; and
a data signal output section to provide gray scales by making the gamma correction to the red data, the green data, and the blue data, based on the plurality of the red gray scale voltages, the green gray scale voltages, and the blue gray scale voltages and to convert the gamma-corrected red data, the gamma-corrected green data, and the gamma-corrected blue data into an analog data red signal, an analog data green signal, and an analog data blue signal.
Also, a preferable mode is one wherein the control circuit feeds the gray scale voltage information by using wirings prepared to supply the red data, the green data, and the blue data to the data electrode driving circuit.
Also, a preferable mode is one wherein a number of counts of clocks used to capture the red data, the green data, and the blue data in the data electrode driving circuit, is associated, in a one-to-one relationship, with an order in which the gray scale voltage information about the red data, the green data, and the blue data is fed to the data electrode driving circuit and wherein the number of counts of clocks is used as the gray scale information.
Also, a preferable mode is one wherein each of the data electrode driving sections includes:
a red gray scale voltage information storing section to store, in advance, a selection signal to provide an instruction as to which gray scale voltage should be selected as a plurality of the red gray scale voltages for the red data;
a green gray scale voltage information storing section to store, in advance, a selection signal to provide an instruction as to which gray scale voltage should be selected as a plurality of the green gray scale voltages for the green data;
a blue gray scale voltage information storing section to store, in advance, a selection signal to provide an instruction as to which gray scale voltage should be selected as a plurality of the blue gray scale voltages for the blue data;
a gray scale information count section to count a number of supplied clocks and to output selection information to provide an instruction as to which gray scale voltage should be selected out of a plurality of the gray scale voltages according to the number of counts of the clocks;
a multiplexer to select any one of gray scale voltages based on the selection signal read from the red gray scale information storing section, the green gray scale information storing section, and the blue gray scale information storing section according to the selection information and to output the selected gray scale voltage as a plurality of red gray scale voltages, a plurality of green gray scale voltages, and a plurality of blue gray scale voltages; and
a data signal output section to provide gray scales by making the gamma correction to the red data, the green data, and the blue data based on the plurality of the red gray scale voltages, the green gray scale voltages, and the blue gray scale voltages and to convert the gamma-corrected red data, the gamma-corrected green data, and the gamma-corrected blue data into an analog data red signal, an analog data green signal, and an analog data blue signal, such that the analog data red signal, the analog data green signal, and the analog data blue signal are output.
Also, a preferable mode is one wherein the gamma correction includes the gamma correction which is made in order to arbitrarily provide a characteristic of luminance required in reproduced images to luminance of input images.
According to a third aspect of the present invention, there is provided a display device having a driving circuit of a color liquid crystal display including:
a data electrode driving circuit to drive the color liquid crystal display by using a gray scale voltage selected based on a video signal out of a plurality of gray scale voltages; and
wherein the data electrode driving circuit produces a plurality of the gray scale voltages corresponding to a gray scale voltage characteristic based on digital gray scale voltage setting data to be supplied.
According to a fourth aspect of the present invention, there is provided a display device having a driving circuit of a color liquid crystal display for driving the color liquid crystal display by using a data red signal, a data green signal, and a data blue signal obtained by making an individual gamma correction to red data, green data, and blue data being digital video data in order to make corrections so that each of the red data, the green data, and the blue data matches a transmittance characteristic of each of a red color, a green color, and a blue color for a voltage applied in the color liquid crystal display, the driving circuit including:
a control circuit mounted separately from the color liquid crystal display and to output, during an invalid period having no bearing on a displaying period for the digital video data, information about the gamma correction to be made to the red data, the green data, and the blue data; and
a data electrode driving circuit mounted in a vicinity of the color liquid crystal display and to drive the color liquid crystal display by using the data red signal, the data green signal, and the data blue signal obtained by making the gamma correction to the red data, the green data, and the blue data, based on information about the gamma correction to be made to the red data, the green data, and the blue data.
According to a fifth aspect of the present invention, there is provided a method for driving a color liquid crystal display by using a data red signal, a data green signal, and a data blue signal obtained by making an individual gamma correction to red data, green data, and blue data being digital video data in order to make corrections so that each of the red data, the green data and the blue data matches a transmittance characteristic of each of red, green, and blue colors for a voltage applied in the color liquid crystal display, the method including:
a step of feeding, from a control circuit mounted separately from the color liquid crystal display, during an invalid period having no bearing on a displaying period for the digital video data, information about the gamma correction to be made to the red data, the green data, and the blue data, to a data electrode driving circuit mounted in a vicinity of the color liquid crystal display and to drive the color liquid crystal display by using the data red signal, the data green signal, and the data blue signal obtained by making the gamma correction to the red data, the green data, and the blue data, based on information about the gamma correction to be made to the red data, the green data, and the blue data.
With the above configurations, the driving circuit of the color liquid crystal display incorporates the data electrode driving circuit adapted to drive the color liquid crystal display using the gray scale voltage selected based on the video signals out of a plurality of gray scale voltages and the data electrode driving circuit is so configured that a plurality of the gray scale voltages being able to correspond to gray scale voltage characteristics is produced based on digital gray scale voltage setting data and, therefore, the substrate packaging area can be reduced and even if the resolution of the color liquid crystal display and/or the number of the gray scale voltages are different, the common substrate and/or TCP can be used, which enables the substrate and/or TCP, that is, the display device to be manufactured at low costs.
With another configuration as above, during the invalid period having no bearing on the displaying period of the digital video data, information about the gamma correction to be made to the red data, the green data, and the blue data is transmitted serially from the control circuit mounted separately from the color liquid crystal display to the data electrode driving circuit adapted to drive the color liquid crystal display and, therefore, the number of wirings required to connect the control circuit to the data electrode driving circuit can be reduced.
With still another configuration as above, the information about the gamma correction to be made to the red data, the green data, and the blue data, during the invalid period, is supplied by using wirings prepared to feed the red data, the green data, and the blue data to the data electrode driving circuit and, therefore, effective use of the wirings is made possible.
With still another configuration as above, the red gray scale voltage, the green gray scale voltage, and the blue gray scale voltage can be set in one operation and, therefore, the processing is made simple and the time required for the setting can be shortened.